linux-kernel - [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in kvm_arch_commit_memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <44edcde46d12c2f5376a1cd1429650acb506ebaf.1637884349.git.maciej.szmigiero@oracle.com>
Date:   Fri, 26 Nov 2021 01:31:07 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Igor Mammedov <imammedo@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in kvm_arch_commit_memory_region()

From: "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>

With kvm->nr_memslot_pages capped at ULONG_MAX we can't safely multiply it
by KVM_PERMILLE_MMU_PAGES (20) since this operation can possibly overflow
an unsigned long variable.

Rewrite this "* 20 / 1000" operation as "/ 50" instead to avoid such
overflow.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 arch/x86/kvm/x86.c              | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1fcb345bc107..8cd1d254c948 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -135,7 +135,7 @@
 #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
 #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
 
-#define KVM_PERMILLE_MMU_PAGES 20
+#define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
 #define KVM_MIN_ALLOC_MMU_PAGES 64UL
 #define KVM_MMU_HASH_SHIFT 12
 #define KVM_NUM_MMU_PAGES (1 << KVM_MMU_HASH_SHIFT)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 04e8dabc187d..69330b395f12 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11753,8 +11753,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
 		unsigned long nr_mmu_pages;
 
-		nr_mmu_pages = kvm->nr_memslot_pages * KVM_PERMILLE_MMU_PAGES;
-		nr_mmu_pages /= 1000;
+		nr_mmu_pages = kvm->nr_memslot_pages / KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO;
 		nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
 		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
 	}